Motion transmitting cable assemblies are typically used for the transmission of force and/or motion from one location to another in apparatus such as automobiles, aircraft, marine craft, motorcycles and bicycles. Such cable assemblies, typically comprising a cable for transmitting the appropriate force or motion and a conduit through which the cable is guided, are used in connection with the various critical components of the aforementioned apparatus, such as throttles, clutches and brakes, as well as a variety of accessories such as air conditioners, heaters, vents, side view mirrors, and the like. It will be understood that as used herein, motion transmitting cable assemblies shall mean extruded and molded tubular products such as push-pull, push-push, pull-pull and rotary cable assemblies and the like, as well as combinations and variations thereof.
Motion transmitting cable assemblies involve a variety of movements of the cable relative to the surrounding conduit including unidirectional, reciprocal, rotary, and combinations of these. Moreover, the movements of the cable relative to the surrounding conduit may range widely in rate, degree and constancy as well as the load under which such movements occur. As a result of these movements, the internal surface of the conduit surrounding the cable is subjected to repeated contact and abrasion by the cable. As used herein, abrasion will refer to the types of damage resulting to the internal surfaces of the articles of the present invention due to the relative movement of cables running therethrough.
It will be appreciated that reliable operation of motion transmitting cable assemblies over extended periods of use is both desirable and critical to the safety of vehicles employing such assemblies. Consequently, in order to achieve superior or even acceptable cable assembly life, conduits have heretofore been constructed with abrasion resistant liners, have employed lubricants and protective outer wrappings or casings, and have utilized combinations of these measures.
Fluorocarbon polymers, such as PTFE resins, are well known in the art and have heretofore been utilized in extruded and molded products such as motion transmitting cable assemblies and the like. In their pure form, PTFE resins exhibit excellent frictional efficiencies. In such form, however, PTFE resins generally exhibit unacceptably low abrasion and creep resistance. As a result, attempts have been made to improve the abrasion and creep resistance of PTFE resins by the addition of organic and inorganic materials as fillers.
It is well known in the art to enhance the abrasion resistance of polymeric products, particularly PTFE extruded products such as conduits, by the inclusion of inert, inorganic fillers such as glass fibers, carbon, asbestos fibers, mica, metals and metal oxides. See, for example, U.S. Pat. No. 3,409,584—Buschman, et al. While a measure of improvement in abrasion resistance has thus been achieved, applicant has recognized that PTFE composites comprising inorganic fillers have continued to display several disadvantages.
The inclusion of inorganic fillers in PTFE conduits for motion transmitting cable assemblies generally lowers the frictional efficiency of such conduits. Further, such inorganically filled articles tend to exhibit rapid deterioration in frictional efficiency after relatively short periods of use. Moreover, the use of lubricants to counteract the loss of frictional efficiency in such conduits is not generally recommended because the inorganic fillers have been found to separate from the composite matrix and form an abrasive slurry with the lubricant. This abrasive slurry not only decreases frictional efficiency of the conduit, but also can cause rapid and catastrophic failure thereof. As a practical result, therefore, it has not been heretofore possible to use inorganically filled PTFE composites in motion transmitting cable assemblies and achieve sustainable high frictional efficiencies.
Fluorocarbon polymers have also been modified to include organic fillers. See, for example, U.S. Pat. No. 3,652,409—Mack et al., and U.S. Pat. No. 4,362,069—Giatras et al. Generally, such organic fillers suitable for use in fluorocarbon polymer conduits are expensive and render the resultant article economically disadvantageous. Further, where organically filled fluorocarbon polymer conduits have been used acceptably they have required relatively expensive and cumbersome outer casings, such as lay wires or steel ribbon wrapping helically wound thereabout, in order to protect the abrasion-resistant material incorporated therein.
Due to the limitations found in the prior art, abrasion resistance in motion transmitting cables has heretofore been limited. Applicant has surprisingly and unexpectedly found that a multi-wall conduit comprising at least an inner wall and an outer wall wherein the inner wall comprises PTFE and the outer wall comprises a composition of PTFE and an inorganic filler yields an article which exhibits superior abrasion resistance. In certain preferred embodiments, the inner wall further comprises an organic filler to further enhance abrasion resistance. The articles of the present invention also provide the additional benefits of superior crush and creep resistance as well. The articles of the present invention are particularly well adapted for use in motion transmitting cable assemblies and the like.
Accordingly, it is an object of the present invention to provide an abrasion resistant multi-wall conduit.
It is another object of the present invention to provide an abrasion resistant multi-wall conduit adapted for use in motion transmitting cable assemblies and the like.
It is yet another object of the present invention to provide an abrasion resistant multi-wall conduit adapted for use in motion transmitting cable assemblies and the like having superior crush and creep resistance.
Still other objects of the invention will be apparent to those of ordinary skill in the art and upon consideration of the following description of the invention.